Dictionary Definition
dim adj
1 lacking in light; not bright or harsh; "a dim
light beside the bed"; "subdued lights and soft music" [syn:
subdued]
2 lacking clarity or distinctness; "a dim figure
in the distance"; "only a faint recollection"; "shadowy figures in
the gloom"; "saw a vague outline of a building through the fog"; "a
few wispy memories of childhood" [syn: faint, shadowy, vague, wispy]
3 made dim or less bright; "the dimmed
houselights brought a hush of anticipation"; "dimmed headlights";
"we like dimmed lights when we have dinner" [syn: dimmed] [ant: undimmed]
4 offering little or no hope; "the future looked
black"; "prospects were bleak"; "Life in the Aran Islands has
always been bleak and difficult"- J.M.Synge; "took a dim view of
things" [syn: black,
bleak]
5 slow to learn or understand; lacking
intellectual acuity; "so dense he never understands anything I say
to him"; "never met anyone quite so dim"; "although dull at
classical learning, at mathematics he was uncommonly quick"-
Thackeray; "dumb officials make some really dumb decisions"; "he
was either normally stupid or being deliberately obtuse"; "worked
with the slow students" [syn: dense, dull, dumb, obtuse, slow]
Verb
1 switch (a car's headlights) from a higher to a
lower beam [syn: dip]
2 become or make darker; "The screen darkend";
"He darkened the colors by adding brown" [syn: darken] [ant: brighten]
3 become dim or lusterless; "the lights dimmed
and the curtain rose"
4 make dim or lusterless; "Time had dimmed the
silver"
5 make dim by comparison or conceal [syn:
blind]
6 become vague or indistinct; "The distinction
between the two theories blurred" [syn: blur, slur] [ant: focus] [also: dimming, dimmed, dimmest, dimmer]dimmer n : a rheostat that
varies the current through an electric light in order to control
the level of illuminationdimmer See dim
User Contributed Dictionary
Noun
Translations
Rheostat
- German: Dimmer
Related terms
Adjective
dimmer- comparative of dim
Extensive Definition
- For the New Zealand band, see Dimmer (band)
Dimmers range in size from small units the size
of a normal light switch used for domestic lighting to high power
units used in large theatre or architectural
lighting installations. Small domestic dimmers are generally
directly controlled, although remote control systems (such as
X10)
are available. Modern professional dimmers are generally controlled
by a digital control system like DMX.
In the professional lighting industry changes in
intensity are called “fades” and can be “fades up” or “fades down”.
Dimmers with direct manual control had a limit on the speed they
could be varied at but this issue is pretty much gone with modern
digital units (although very fast changes in brightness may still
be avoided for other reasons like lamp life).
Modern dimmers are built from silicon-controlled
rectifiers (SCR) instead of potentiometers or variable
resistors because they have higher efficiency.
A variable resistor would dissipate power by heat (efficiency as
low as 0.5). By switching on and off, theoretically a
silicon-controlled rectifier dimmer does not heat up (efficiency
close to 1.0).
History
One of the earliest recorded dimmers is Granville Woods's "Safety Dimmer", published in 1890; dimmers before that were liable to cause fires.Early dimmers were directly controlled through
the manual manipulation of large dimmer panels, but this meant that
all power had to come through the lighting control location, which
could be inconvenient and potentially dangerous, especially with
systems that had a large number of channels, high power lights or
both (such as a stage
disco or other similar
venues).
When thyristor dimmers came into
use, analog remote control systems (often 0-10V
lighting control systems) became feasible. The wire for the
control systems was much smaller (with low current and lower
danger) than the heavy power cables of previous lighting systems.
Each dimmer had its own control wires which meant a huge number of
wires leaving the lighting control location and running to each
individual dimmer. Modern systems use a digital control protocol
such as DMX512 to
control a large number of dimmers (and other stage equipment)
through a single cable.
In 1961 Joel Spira, founder of Lutron Electronics,
invented the first solid state dimmer, which switches the current
on and off 120 times per second, saving energy and allowing the
dimmer to be installed in a standard electrical wallbox.
Types of dimmer
Early examples of a dimmer include a salt water dimmer. In a salt water dimmer, there were two metal contacts in a glass beaker. One contact was on the bottom, while the other was able to move up and down. The closer the contacts to each other, the higher the level of the light. Using salt water dimmers was a tedious and precarious task that included filling the beakers with water, checking the concentration of the salt, and raising or lowering the top contact. Salt water dimmers were not efficient due to the evaporation of water and the corrosion of the many metal pieces. These dimmers were colloquially known as "pis pots", for obvious reasons. Many old theatre electricians still recount stories of how they were initiated into the art by being requested to "top up a pot" and receiving a shock, as unbeknownst to them the pot was live...Thyristor (and
briefly, thyratron)
dimmers were introduced to solve some of these problems. Because
they use switching techniques instead of potential division there
is almost no wasted power, dimming can be almost instantaneous and
is easily controlled by remote electronics. Triacs are used
instead of SCR
thyristors in lower cost designs, but do not have the surge
handling capacity of back-to-back SCR's, and are only suitable for
loads less than about 20 Amps. The switches generate some heat
during switching, and can cause interference.
Large inductors are
used as part of the circuitry to suppress this interference. When
the dimmer is at 50% power the switches are switching their highest
voltage (>300 V in Europe) and the sudden surge of power causes
the coils on the inductor to move, creating buzzing sound
associated with some types of dimmer; this same effect can be heard
in the filaments
of the incandescent
lamps as "singing". The suppression circuitry adds a lot of
weight to the dimmer, and is often insufficient to prevent buzzing
to be heard on audio systems that share the mains supply with the
lighting loads. This development also made it possible to make
dimmers small enough to be used in place of normal domestic light
switches. European dimmers must comply with relevant EMC legislation
requirements; this involves suppressing the emissions described
above to limits described in EN55104.
An alternative to the leading-edge dimming that
is typically used with SCRs is trailing edge dimming, where the
falling part of the waveform is cut rather than the rising part.
This is most often used in devices that use a switched-mode
power supplies that need the front of the waveform complete so
that it may cut itself.
Sine-wave dimming promises to solve the weight
and interference issues that afflict thyristor dimmers. These are
effectively high power switched-mode
power supplies. They rely on a new generation of insulated
gate bipolar transistors (IGBTs)
which are still relatively expensive.
Control
see also Lighting
control console
Non domestic dimmers are usually controlled
remotely by means of various protocols. Analogue dimmers usually
require a separate wire for each channel of dimming carrying a
voltage
between 0
and 10 V. Some analogue circuitry then derives a control signal
from this and the mains supply for the switches. As more channels
are added to the system more wires are needed between the lighting
controller and the dimmers.
In the late 70s serial analogue protocols were
developed. These multiplexed a series of analogue levels onto a
single wire, with embedded clocking signal similar to a composite
video signal (in the case of Strand Lighting's European D54 standard, handling
384 dimmers) or separate clocking signal (in the case of the US
standard AMX192).
Digital protocols, such as DMX512
have proved to be the answer since the late 80s. In early
implementations a digital signal was sent from the controller to a
demultiplexer, which sat next to the dimmers. This converted the
digital signal into a collection of 0 to +10 V or 0 to -10 V
signals which could be connected to the individual analogue control
circuits.
Modern dimmer designs use microprocessors to
convert the digital signal directly into a control signal for the
switches. This has many advantages, giving closer control over the
dimming, and giving the opportunity for diagnostic feedback to be
sent digitally back to the lighting controller.
Patching
Preheat
Some types of incandescent (filament) lamps should not be switched to full power from cold, and doing so can shorten their life dramatically owing to the large inrush current that occurs. To soften the blow to the lamps slightly, dimmers may have a preheat function. This sets a minimum level, usually between 5% and 10%, which is not obvious to the audience, but stops the lamp from cooling down too much. This also speeds up the lamp's reaction to sudden bursts of power that operators of rock'n'roll-style shows appreciate. The opposite of this function is sometimes called top-set. This limits the maximum power supplied to a lamp, which can also extend its life.The digital revolution
Modern digital desks can emulate preheat and dimmer curves and allow a soft patch to be done in memory. This is often preferred as it means that the dimmer rack can be exchanged for another one without having to transfer complicated settings. Many different curves, or profiles can be programmed and used on different channels.Rise time
One measure of the quality of the dimmer is the "rise time". The rise time in this context is the amount of time it takes within the cut part of the waveform to get from the zero-point crossover to the start of the uncut part of the waveform. A longer rise time reduces the noise of the dimmer and the lamp as well as extending the life of the lamp. Unsurprisingly, a longer rise time is more expensive to implement than a short one, this is because the size of choke has to be increased.See also
References
- Bellman, Wilard F. (2001). LIGHTING THE STAGE: Art and Practice, Third Edition, Chapter 4 –The Control Console, Broadway Press, Inc., Louisville Kentucky, ISBN 0-911747-40-0
External links
dimmer in German: Dimmer
dimmer in Spanish: Dimmer
dimmer in French: Gradateur
dimmer in Italian: Dimmer
dimmer in Dutch: Dimmer
dimmer in Russian: Диммер
dimmer in Finnish: Himmennin
dimmer in Turkish: Dimmer
dimmer in Ukrainian: Регулятор
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